In a liquid chromatograph mass spectrometer, which uses a mass spectrometer as a detector for a liquid chromatograph, an atmospheric pressure ion source is used to ionize a liquid sample. Such an atmospheric pressure ion source uses an electrospray ionization method, atmospheric pressure chemical ionization method, or other methods. During an analysis, the eluate from a column of a liquid chromatograph is introduced into a mass spectrometer. On the other hand, when a tuning for each unit of the mass spectrometer is performed, a standard sample composed of components whose kinds and concentrations are known is directly introduced into the mass spectrometer. “Tuning” as used herein refers to optimally setting conditions such as voltages applied to each unit and the temperature of an ionization probe in order to perform an m/z value calibration, adjustment of the mass resolution, adjustment of the sensitivity, and other conditions.
One known method for directly introducing a standard sample into an atmospheric pressure ion source is a pressurized liquid feeding method. In the pressurized liquid feeding method, a gas at a certain pressure is introduced via a pressurization tube into an in-chamber space above the liquid surface of a closed chamber which contains a standard sample (or solution). This gas presses down the liquid level of the standard sample, and the standard sample is supplied to the outside of the chamber by way of a liquid feeding tube extending from below the liquid surface (refer to Patent Document 1).
In recent years, the configuration of a mass spectrometer has become very complicated, and also the number of units and items that have to be tuned has been increasing. Consequently, the time required for tuning has become longer. In such circumstances, it has been found that spike-like noises are generated in a detected signal in the case where a standard sample is introduced by using a sample introduction apparatus by a pressurized liquid feeding method as previously described. The longer the time to perform the pressurized liquid feeding is, the more noticeable such spike-like noises become. The effect of the noise may be insignificant when the time required for tuning is short; however, when the tuning time becomes long, the noise causes serious problems, such as disturbing the appropriate tuning.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2008-14788